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The High Concentration Photovoltaic Thermal: coming to a neighborhood near you.


The High Concentration PhotoVoltaic Thermal (HCPVT) system uses a large mirrored parabolic dish attached to a tracking system to position the dish at an optimal angle to the sun. The HCPVT system concentrates solar radiation 2,000 times and converts 80 percent of the incoming radiation into useful energy.

- High Concentration PhotoVoltaic Thermal system able to convert 80% of the sun’s energy. 
- System can deliver electricity and potable water in remote locations.
- Design based on a large dish-like concentrator and cooled photovoltaic chips.

A team of researchers are working on a solar concentrating dish that will be able to collect 80% of incoming sunlight and convert it to useful energy. The High Concentration Photovoltaic Thermal system will be able to concentrate the power of 2,000 suns. As an added bonus, the researchers state that the system would be able to supply fresh water and cool air wherever it is built at one third the cost of current comparable technologies. A $2.4 million grant from the Swiss Commission for Technology and Innovation has been awarded to develop the system. IBM, Airlight Energy, ETH Zurich and Interstate University of Applied Sciences will all be developing the prototypes and various components. A prototype of the HCPVT system is currently being tested at IBM Research - Zurich. Additional prototypes will be built in Biasca and Rueschlikon, Switzerland as part of the collaboration. 

"We plan to use triple-junction photovoltaic cells on a micro-channel cooled module which can directly convert more than 30 percent of collected solar radiation into electrical energy and allow for the efficient recovery of an additional 50 percent waste heat," said Bruno Michel, manager, advanced thermal packaging at IBM Research. "We believe that we can achieve this with a very practical design that is made of lightweight and high strength concrete, which is used in bridges, and primary optics composed of inexpensive pneumatic mirrors -- it's frugal innovation, but builds on decades of experience in microtechnology. 

"The design of the system is elegantly simple," said Andrea Pedretti, chief technology officer at Airlight Energy. "We replace expensive steel and glass with low cost concrete and simple pressurized metalized foils. The small high-tech components, in particular the microchannel coolers and the molds, can be manufactured in Switzerland with the remaining construction and assembly done at the installation. This leads to a win-win situation where the system is cost competitive and jobs are created in both regions." 

The solar concentrating optics will be developed by ETH Zurich. "Advanced ray-tracing numerical techniques will be applied to optimize the design of the optical configuration and reach uniform solar fluxes exceeding 2,000 suns at the surface of the photovoltaic cell," said Aldo Steinfeld, Professor at ETH Zurich. 

"Microtechnology as known from computer chip manufacturing is crucial to enable such an efficient thermal transfer from the photovoltaic chip over to the cooling liquid," said Andre Bernard, head of the MNT Institute at NTB Buchs. "And by using innovative ways to fabricate these heat transfer devices we aim at a cost-efficient production." 



The sun's rays are reflected off the mirrors onto liquid cooled photovoltaic chips; with each chip able to generate 200-250 watt hours over an eight hour day in a sunny region. More than 30 percent of collected solar radiation can be converted into electrical energy and the hundreds of chips in each unit collectively represent 25 kilowatts of electricity generation capacity. The researchers believe they can achieve a cost per aperture area below $250 per square meter, with a levelised cost of energy less than 10 cents per kilowatt hour. 

The HCPVT system is designed around a huge parabolic dish covered in mirror facets. The dish is supported and controlled by a tracking system that moves along with the sun. Sun rays reflect off of the mirror into receivers containing triple junction photovoltaic chips, each able to convert 200-250 watts over eight hours. Combined hundred of the chips provide 25 kilowatts of electricity. Replacing expensive steel and glass with concrete and pressurized foils, the HCPVT is less costly than many other similar installations. Its high tech coolers and molds can be manufactured in Switzerland, and construction provided by individual companies on-site. Through their design, IBM believes they can maintain a cost of less than 10 cents per kilowatt hour.

The entire dish is cooled with liquids that are more effective than passive air methods, keeping the HCPVT safe to operate at a concentration of 2,000 times on average, and up to 5,000 times the power of the sun. The system will also be able to create fresh water by passing heated water through a distillation system that vaporizes and desalinates up to 40 liters each day while still generating electricity. It will also be able to provide air conditioning by a thermal absorption chiller.

The liquid cooling system, 10 times more effective than passive air cooling, keeps the chips at a safe temperatures up to a solar concentration of 5,000 times. The heated liquid presents another opportunity for energy harvesting in heat recovery, with the potential for approximately 50% of the waste heat being utilised. The heated liquid can be used for desalination while still generating electricity.
   
Based on information by the European Electricity Association, IBM claims that it would require only two percent of the Sahara’s total area to supply the world’s energy needs. Cost effective and efficient, the HCPVT system could be vital to developing nations. Remote locations could also benefit from the technology, eliminating the need to build a large integrated infrastructure. Several prototypes of the dish will first be built in Biasca and Rüschlikon, Switzerland.

Background – Today solar photovoltaics (PV) remains the fastest growing power generation technology by installed capacity in the world. Yet, the technology has its limitations, most importantly its low efficiency (around 15% for direct solar irradiation) compared to other power generation technologies. A substantial improvement of this efficiency is obtained by the Concentrating Photovoltaics (CPV) technology. Optical concentrators are used to increase the solar radiation density on the PV cell, which leads to a reduction of cell area needed for the same amount of power production. Since concentrators (e.g. parabolic dishes) use cheaper materials and are often easier to manufacture than PV cells, there is a notable potential for overall cost reductions. Furthermore, CPV uses the more expensive triple junction PV cells that reach comparatively high efficiencies, especially at high solar concentrations. Using the same amount of land, CPV systems can produce more electricity, more efficiently and using much less PV material than conventional PV systems.

While High Concentration PhotoVoltaic (HCPV) systems achieve high conversion efficiencies, the cost of produced electricity remains comparably high. Main reasons are the high cost of involved materials (PV cells and concentrator) and system complexity due to tracking and cooling. An approach to reduce the cost of electricity generation is to utilize the thermal energy harvested during the cooling of the PV cell.

Goal – The goal of the project is to realize a cost-competitive High Concentration PhotoVoltaic Thermal (HCPVT) system able to convert 80% of the collected solar energy into useful electrical and thermal output. Materials for a low-cost large dish-like concentrator and a high performance receiver are exploited for mass-production. The main commercial goal is a solar technology that increases the conversion efficiency from solar-to-electrical beyond 22 percent and allows additional recovery of at least 50% thermal energy. Solar radiation is concentrated 2000 times onto a receiver holding an array of triple junction PV chips able to extract half of the incoming energy as heat while maintaining the solar cells at safe temperatures. 

 A three-year, $2.4 million (2.25 million CHF) grant from the Swiss Commission for Technology and Innovation has been awarded to scientists at IBM Research (NYSE: IBM); Airlight Energy, a supplier of solar power technology; ETH Zurich (Professorship of Renewable Energy Carriers) and Interstate University of Applied Sciences Buchs NTB (Institute for Micro- and Nanotechnology MNT) to research and develop an economical High Concentration PhotoVoltaic Thermal (HCPVT) system.

Based on a study by the European Solar Thermal Electricity Association and Greenpeace International, technically, it would only take two percent of the solar energy from the Sahara Desert to supply the world's electricity needs*. Unfortunately, current solar technologies on the market today are too expensive and slow to produce, require rare Earth minerals and lack the efficiency to make such massive installations practical. 

The prototype HCPVT system uses a large parabolic dish, made from a multitude of mirror facets, which are attached to a sun tracking system. The tracking system positions the dish at the best angle to capture the sun's rays, which then reflect off the mirrors onto several photovoltaic chips -- each chip can convert 50 watts over a eight hour day in a sunny region. The entire receiver combines hundreds of chips and provides 25 kilowatts of electrical power. The photovoltaic chips are mounted on liquid coolants to absorb the heat and draw it away. With such a high concentration and a radically low cost design scientists believe they can achieve a cost three times lower than comparable systems.

Water Desalination and Cool Air

Current concentration photovoltaic systems only collect electrical energy and dissipate the thermal energy to the atmosphere. With the HCPVT packaging approach scientists can both eliminate the overheating problems of solar chips while also repurposing the energy for thermal water desalination and adsorption cooling. 

To capture the medium grade heat IBM scientists and engineers are utilizing an advanced technology they developed for water-cooled high performance computers. With computers water is used to absorb heat from the processor chips, which is then used to provide space heating for the facilities. In the HCPVT system, instead of heating a building, the 90 degree Celsius water will be used to heat salty water that then passes through a distillation system where it is vaporized and desalinated. Such a system could provide 30-40 liters of drinkable water per square meter of receiver area per day, while still generating electricity with a more than 25 percent yield or two kilowatt hours per day -- a little less than half the amount of water the average person needs per day according to the United Nations, but a large installation could provide enough water for a city. 

Remarkably, the HCPVT system can also provide air conditioning by means of a thermal driven absorption chiller. An adsorption chiller is a device that converts heat into cooling via a thermal cycle applied to an absorber made from silica gel, for example. Adsorption chillers, with water as working fluid, can replace compression chillers, which stress electrical grids in hot climates and contain working fluids that are harmful to the ozone layer. 

Scientists envision the HCPVT system providing sustainable energy and potable water to locations around the world including southern Europe, Africa, Arabian peninsula, the southwestern part of the United States, South America, and Australia. Remote tourism locations are also an interesting market, particularly resorts on small islands, such as the Maldives, Seychelles and Mauritius, since conventional systems require separate units, with consequent loss in efficiency and increased cost.